Combination of Extraction by Silylated Vessel-Dispersive Liquid–Liquid Microextraction as a High-Enrichment Factor Technique: Optimization and Application in Preconcentration of Some Triazole Pesticides from Aqueous Samples Followed by GC-FID Determination

This study describes an extraction method based on silylated extraction vessel-dispersive liquid–liquid microextraction (SEV-DLLME) for preconcentration of some triazole pesticides (penconazole, hexaconazole, tebuconazole, diniconazole, triticonazole, and difenconazole) from aqueous samples. For this purpose, the interior surface of funnel-shaped extraction vessel is activated by concentrated NaOH and HCl solutions, silylated by trimethylchlorosilane (TMCS) and used in extraction of the analytes from a relatively high volume of aqueous sample. The adsorbed analytes are desorbed by methanol, which acts as a dispersive solvent in the following DLLME method. In the first step, the effects of different factors i.e., concentrations of NaOH, HCl, and silylated agent and their contact times were studied using central composite design (CCD) and response surface method. Extraction time, extraction solvent (chloroform) volume, dispersive solvent (methanol) volume, centrifugation rate and time, and salting-out effect in DLLME procedure were optimized in the same way using CCD, in the second step. High enrichment factors (EFs) (more than 1,000 in most cases) and low detection limits (at sub μg L^?1 level) are attainable by using gas chromatography-flame ionization detection. The repeatability and reproducibility of the proposed method are good and the relative standard deviations (RSD %) for six repeated experiments (C = 100 μg L^?1 of each pesticide) are less than 7.25%. Finally, the method was successfully applied in determination of analytes in some aqueous samples such as wastewater, well water, and some fruit juice samples.     

General formula for stability testing of linear systems with fractional-delay characteristic equation

In some applications (especially in the filed of control theory) the characteristic equation of system contains fractional powers of the Laplace variable s possibly in combination with exponentials of fractional powers of s. The aim of this paper is to propose an easy-to-use and effective formula for bounded-input boundedoutput (BIBO) stability testing of a linear time-invariant system with fractional-delay characteristic equation in the general form of $\Delta \left( s \right) = P_0 \left( s \right) + \sum\nolimits_{i = 1}^N {P_i \left( s \right)\exp ( - \zeta _i s^{\beta _i } ) = 0}$ , where P _i (s) (i = 0,...,N) are the so-called fractional-order polynomials and ξ _i and β _i are positive real constants. The proposed formula determines the number of the roots of such a characteristic equation in the right half-plane of the first Riemann sheet by applying Rouche’s theorem. Numerical simulations are also presented to confirm the efficiency of the proposed formula.     

Infrared spectroscopic and chemometric approach for identifying binding medium in Sukias mansion’s wall paintings

Abstract

This paper addresses the application of infrared spectroscopy in combination with chemometrics to identify wall painting’s binding medium while employing pattern recognition techniques to process FTIR data-set of complex samples. In this regard, based on the historical documents and previous researches, firstly 56 standard samples were prepared to represent strata of Persian wall paintings in the Safavid period in addition to real historic samples from the case study; Sukias mansion. Then, each sample was analysed by the means of FTIR and chemometrics. Finally, SIMCA was applied to the whole region of studied IR spectra which predicted egg yolk as the binding medium of Sukias mansion samples.     

An Analytical Solution for Capillary Gravity Drainage with Dominant Viscous Forces

The development of the capillary fringe during gravity drainage has a significant influence on saturation and pressure distributions in porous formations (Sarkarfarshi et al. in Int J Greenh Gas Control 23:61–71, 2014). This paper introduces an analytical solution for gravity drainage in an axisymmetric geometry with significant capillary pressure. The drainage process results from the injection of a lighter and less viscous injectant into a porous medium saturated with a heavier and more viscous pore fluid. If the viscous force dominates the capillary and the buoyancy forces, then the flow regime is approximated by differential equations and the admissible solution comprises a front shock wave and a trailing simple wave. In contrast to existing analytical solutions for capillary gravity drainage problems (e.g., Nordbotten and Dahle in 47(2) 2011; Golding et al. in J Fluid Mech 678:248–270 2011), this solution targets the saturation distribution during injection at an earlier point in time. Another contribution of this analytical solution is the incorporation of a completely drained flow regime close to the injection well. The analytical solution demonstrates the strong dependency of the saturation distribution upon relative permeability functions, gas entry capillary pressure, and residual saturation. The analytical results are compared to results from a commercial reservoir engineering software package (\(\hbox {CMG } \hbox {STARS}^{\mathrm{TM}}\)).     

Local thermal non-equilibrium analysis of conjugate free convection within a porous enclosure occupied with Ag–MgO hybrid nanofluid

Current investigation aims to analyze the conjugate free convection inside a porous square cavity occupied with Ag–MgO hybrid nanofluid using the local thermal non-equilibrium (LTNE) model. Hybrid nanofluids are a novel kind of enhanced working fluids, engineered with enhanced thermo-physical and chemical properties. Two solid walls located between the horizontal bounds in two sides of cavity play the role of a conductive interface between the hot and cold walls, and moreover, the top and bottom bounds have been insulated. The governing differential equations are obtained by Darcy model and then for better representation of the results, converted into a dimensionless form. The finite element method is utilized to solve the governing equations. To evaluate the correctness and accuracy of the results, comparisons have been performed between the outcomes of this work and the previously published results. The results indicate that using the hybrid nanoparticles decreases the flow strength and the heat transfer rate. The heat transfer rate augments when R_k rises and the flow strength augments when Ra grows. Enhancing the porosity increases strongly the size and strength of the vortex composed inside the porous medium. When K_r is low, the heat transfer rate is low and by increasing K_r, thermal fields become closer to each other. The effect of hybrid nanoparticles on thermal fields with the thinner solid walls is more than that the thicker ones. An increment in H eventuates the enhancement of heat transfer and hence, the thermal boundary layer thickness. By increasing the volume fraction of the hybrid nanoparticles, Nu_hnf and Nu_s decrease in constant Ra. Besides, increase in Ra enhances the Nu_hnf and Nu_s. For a certain d, the reduction of Nu_s due to using the hybrid nanoparticles is more than that for Nu_hnf. The increment of d lessens Nu_hnf for all values of K_r and has not specific trends for Nu_s. Utilizing hybrid nanoparticles decreases Nu_s (except d?=?0.4), rises Nu_s when K_r?<?18, while it can increase Nu_s for K_r?>?42. In constant d, increment of H, respectively, decreases and boosts Nu_hnf and Nu_s. For all values of d, increment of ε declines Nu_hnf. In low value of d, the increase in ε reduces Nu_s, whereas at higher values, Nu_s has continuously enhancing trend. For different values of d, the increase in ε scrimps Nu_hnf. The increment of d and also ε, and H are, respectively, decreases and increases the heat transfer rate.

     

Enzymatic/Immunoassay Dual‐Biomarker Sensing Chip: Towards Decentralized Insulin/Glucose Detection

Performing bioassay formats based on enzyme and antibody recognition reactions with a single detection chip remains an unmet challenge owing to the different requirements of such bioassays. Herein, we describe a dual‐marker biosensor chip, integrating enzyme and antibody‐based assays for simultaneous electrochemical measurements of insulin (I) and glucose (G). Simultaneous G/I sensing has been realized by addressing key fabrication and operational challenges associated with the different assay requirements and surface chemistry. The I immunosensor relies on a peroxidase‐labeled sandwich immunoassay, while G is monitored through reaction with glucose oxidase. The dual diabetes biomarker chip offers selective and reproducible detection of picomolar I and millimolar G concentrations in a single microliter sample droplet within less than 30 min, including direct measurements in whole blood and saliva samples. The resulting integrated enzymatic‐immunoassay biosensor chip opens a new realm in point‐of‐care multiplexed biomarker detection.     

Polymer friction-transfer layers as orienting substrates

A variety of polymers were investigated as candidates for the formation of oriented layers by friction transfer. Only polyethylene, the liquid-crystalline Vectrá and fluorinated ethylene-propylene copolymer were found to yield oriented transfer layers. These layers, in turn, were found to induce the oriented growth a variety of species deposited onto them from the melt, solution or vapor phase. The present orientation-inducing friction-transfer layers, however, were found to be inferior to those of poly(tetrafluoroethylene) [PTFE], described previously. © 1994 John Wiley & Sons, Inc.     

Optimizing refolding and recovery of active recombinant Bacillus halodurans xylanase in polymer-salt aqueous two-phase system using surface response analysis

An experimental design was used to determine optimal conditions for refolding of a recombinant thermostable and alkaline active xylanase from Bacillus halodurans in PEG-phosphate two-phase system. The influence of different experimental variables on the enzyme recovery has been evaluated. To build the mathematical model and minimize the number of experiments for the design parameters, response surface methodology with a face-centered central composite design (CCF) was defined based on the conditions found by preliminary tests that resulted in the highest refolding yield. The adequacy of the calculated model for the response was confirmed by means of variance analysis and additional experiments. Analysis of contours of constant response as a function of pH, polyethylene glycol (PEG) molecular weight and concentration, and salt concentration for different enzyme loads revealed different effects of these five factors on the studied parameters. Recovery of more than 92% active xylanase was predicted for a system with 18.3% (w/w) PEG 1000, 14.4% (w/w) phosphate at pH 8.5, and enzyme load corresponding to a protein concentration of about 0.05 mg/g system. The yield of the refolded enzyme was found to be optimal at 22 degrees C. The validity of the response model was verified by a good agreement between predicted and experimental results.